unsigned long currentMillis = 0;
unsigned long previousMillis = 0;

bool firstClick;

void setup() {
  Serial.begin(115200);
}

void loop() {
  if (digitalRead(3)) {
    currentMillis = millis();
    if (currentMillis - previousMillis >= 200 && !digitalRead(3)) {
      //oneclick
      Serial.print("1");
      previousMillis = currentMillis;
      firstClick = true;

    } else if (currentMillis - previousMillis >= 200 && digitalRead(3)) {
      //DoubleClick
      Serial.print("2");
      previousMillis = currentMillis;
      firstClick = false;

    } else if (currentMillis - previousMillis >= 2000 && digitalRead(3)) {
      //long click (hold for 2000 ms or 2s)
      Serial.print("3");
      previousMillis = currentMillis;
    }
    firstClick = false;
  }
}